Chapter 24: Chemical Communications: Neurotransmitters and Hormones

A set of vocabulary flashcards covering the chemical communication terms, messenger classes, and signal transduction mechanisms described in the Chapter 24 lecture notes.

Neuron

A nerve cell.

Neurotransmitter

A chemical messenger between a neuron and another target cell such as a neuron, muscle cell or cell of a gland.

Hormone

A chemical messenger released by an endocrine gland into the bloodstream and transported there to reach its target cell.

Antagonist

A molecule that blocks a natural receptor and prevents its stimulation.

Agonist

A molecule that competes with a natural messenger for a receptor site, binds to it, and elicits the same response as the natural messenger.

Acetylcholine (ACh)

The main cholinergic messenger stored in vesicles; it is released when $Ca^{2+}$ concentration increases to more than about $0.1\,mM$.

Nicotinic receptors

Receptors for acetylcholine found in motor end plates of skeletal muscles or in sympathetic ganglia; they are inhibited by nicotine.

Acetylcholinesterase

The enzyme that catalyzes the hydrolysis of acetylcholine for its rapid removal from the receptor site, allowing for more than $100$ signals per second.

Phosphonates

Compounds in nerve gases and some pesticides that inhibit acetylcholinesterase irreversibly.

Ligand-gated ion channels

Ion channels that open and propagate signals in response to the binding of a ligand, such as acetylcholine, to a receptor.

Nicotine (pharmacological effect)

Acts as an agonist in low doses to prolong a receptor's response, but acts as an antagonist in large doses to block the receptor.

Excitatory neurotransmitters

Amino acids that stimulate neurotransmission, such as Glu, Asp, and Cys.

Inhibitory neurotransmitters

Amino acids that reduce neurotransmission, such as Gly.

NMDA receptor

N-methyl-D-aspartate receptor; a ligand-gated ion channel and subclass of Glu receptors whose gate is closed by $Mg^{2+}$ ion.

G-protein

A protein that hydrolyzes GTP to provide energy for activating adenylate cyclase in response to norepinephrine absorption.

Adenylate cyclase

An enzyme activated by G-protein that catalyzes the synthesis of cAMP from ATP.

Cyclic AMP (cAMP)

A secondary messenger that activates protein kinase by dissociating its regulatory (R) unit from its catalytic (C) unit.

Protein kinase

An enzyme activated by cAMP that phosphorylates ion-translocating proteins or other enzymes to control their activity.

Phosphodiesterase

The enzyme that destroys existing cAMP by catalyzing the hydrolysis of a phosphodiester bond to produce AMP.

Monoamine oxidases (MAOs)

Enzymes that inactivate monoamine messengers by catalyzing their oxidation to an aldehyde.

Histamine

A monoamine synthesized from His by decarboxylation that acts on H1 and H2 receptors.

H1 receptors

Receptors found in the respiratory tract involved in vascular, muscular, and secretory changes related to hay fever and asthma.

H2 receptors

Receptors found mainly in the stomach that affect the secretion of HCl and are blocked by drugs like cimetidine and ranitidine.

Enkephalins

Pentapeptides present in certain nerve cell terminals that bind to specific pain receptors to control pain perception.

Neuropeptide Y

A potent orexic peptide that affects the hypothalamus.

Substance P

An $11$-amino acid peptide involved in the transmission of pain signals.

Steroid messengers

Hydrophobic hormones that cross plasma membranes by diffusion and interact with protein receptors inside the nucleus or cytoplasm.